The present invention relates to a thin-film coating technique and, more particularly, relates to a technique which effectively serves as a thin-film coating technique for coating a surface of a substrate with a thin film.
Prior Art
Generally, printed circuit boards used in electronic appliances, such as computers or the like, are provided by forming a patterned working of copper or the like on one side or opposite sides of an insulating substrate.
Printed circuit boards of this type can be produced by the following manufacturing process:
First, a lamination composed of a light-sensitive resin (photoresist) layer and a light-transmissive resin film (protective layer) for protecting the light-sensitive resin layer are laminated by thermocompression-bonding onto an electrically conductive layer (copper thin film) provided on an insulating substrate. The thermocompression-bonding lamination is mass-produced by a thin-film coating apparatus called a "laminator". After thermocompression-bonding lamination, a wiring pattern film is overlapped on the lamination and the light-sensitive resin layer is exposed to light for a predetermined period of time through the wiring pattern film and the transmissive resin film. After the transmissive resin film is parted from the substrate by film removing apparatus, the exposed light-sensitive resin layer is developed to form an etching mask pattern. After development, the unnecessary portion of the electrically conductive layer is removed by etching and then the residual part of the light-sensitive resin layer is removed, so that a printed circuit board having a predetermined wiring pattern is prepared.
As described above, according to the conventional thin-film coating method, a lamination composed of a light-sensitive resin (photoresist) layer and a light-transmissive resin film (protective layer) is thermocompression-bonded onto an electrically conductive layer (copper thin film) provided on an insulating substrate. However, the surface of the electrically conductive layer has a slight surface roughness, such that air pockets are formed on the slightly uneven surface of the electrically conductive layer when laminated with the laminated film. Thus, void spaces occur at the contacting surface between the electrically conductive layer and the lamination. Accordingly, the conventional thin-film coating method has a problem in that the adhesion between the electrically conductive layer and the lamination deteriorates, causing a further problem in that the reliability on the wiring of the printed circuit board is lowered.